In recent years, a technique of updating the memory contents of the first and second non-volatile memory in a control unit is proposed. In the proposed technique, the control unit for storing a control program in the first memory in a course of controlling a controlled object, and for storing event codes generated in the course of control of the controlled object performs, as an update process of the control program stored in the first memory is performed, initialization of all of the memory areas in the second memory. The technique is disclosed in, for example, Japanese patent documents JP-A-2002-323990 and JP-A-2004-118445.
However, the above technique deletes all event codes stored in the second memory in the process of updating the control program stored in the first memory. Therefore, the deleted event codes can not be referred to after the deletion.
If all memory areas in the second memory are configured not to be initialized in the process of updating the control program in the first memory, the event code corresponding to an event that will not be generated any more by the updated control program may be left unchanged in the second memory.
The event code corresponding to the event that will not be generated any more by the updated control program is considered as less necessary or un-necessary for reference, and is desirable to be identified. By identifying the un-necessary event code, the event code can be easily deleted, for example.